This invention relates generally to radio receivers and, more particularly to an improvement in a portable radio transceiver which significantly lowers the power consumption thereof.
In portable radio receivers and/or transceiver, a battery is generally utilized as the power supply. Accordingly, it is desirable to utilize a circuit construction which minimizes the power consumption where possible, in order to lengthen the service life of the battery.
Conventional radio receivers or transceivers generally include a squelch circuit for feeding the received audio signal to the audio amplifier system only when an audio signal sufficiently above the background noise level is present in the incoming radio signal. However, conventional audio amplifiers and preamplifiers generally draw a considerable amount of power even when no audio signal is being amplified, without regard for the action of the squelch circuit. For example, in a typical class B push-pull amplifier it is necessary to apply an idling current of about 5 to 10 mA in order to prevent crossover distortion even when no audio signal is present. Additionally, typical preamplifier circuits generally draw between 5 to 7 mA when no audio signal is present.
The provision of a squelch circuit prevents noise from being amplified and reproduced at the speakers of the receiver by detecting the level of noise present in the absence of an incoming radio signal and cutting off the inputs to the audio preamplifier and amplifier system when this noise exceeds a preselected level. However, this cutting off of the audio signal has little effect upon the power consumption of the audio amplifier circuits due to the idling current supplied to these circuits as mentioned above. Consequently, conventional radio receivers and transceivers exhibit significant power consumption even when no audio output is being produced. In a portable, battery powered unit, this amount of power consumption is undesirable in that it is deleterious to the batteries.